The present invention relates to a headway control system and, more particularly, to a headway control system provided with a traffic congestion following processing function.
A traffic congestion following device that allows a host vehicle to follow a preceding vehicle in heavy traffic is known. A common traffic congestion following device is provided with a function that detects a headway distance and a function that controls the host vehicle so as to move it forward or bring it to a stop. It performs a following processing to adjust the headway distance to an appropriate value. Two types of following processing are known. One is a fully automatic system, in which the host vehicle starts moving automatically as soon as the preceding vehicle moves forward. The other is a semi-automatic system that does not immediately perform the following processing even when the preceding vehicle moves forward, requiring intervention by a driver through switch operation as a trigger.
Japanese Utility Model Laid-open No. 3-68126 discloses a manually operated switch that is operated by the driver to perform the following processing in the semiautomatic system. Japanese Patent Laid-open No. 2000-118261 discloses an approach, in which an accelerator pedal is used as the switch to facilitate operation of the driver.
The manually operated switch, however, means that it necessary to provide a new switch. Moreover, it requires that the driver perform an operation in addition to driving the vehicle, which bothers the driver.
With the prior art, in which the accelerator pedal is used as the switch, it is difficult to set how much the accelerator pedal is to be depressed to determine that the switch is actuated. That is, it is difficult to establish a relationship between an accelerator pedal stroke and ON/OFF position of the switch.
In ordinary operations of vehicles, the accelerator pedal is used as a means of increasing the vehicle speed. The more the driver depresses the accelerator pedal, the higher the engine speed and thus the vehicle speed. Using the accelerator pedal as the switch gives the pedal a new function that is different from driving. Suppose that there is a preceding vehicle running immediately in front of the host vehicle in heavy traffic. Even while the following processing device is being activated, the driver is likely to feel hesitant about depressing the accelerator pedal hard when he or she is afraid that doing that could jump the host vehicle forward. It is thus difficult to set a large pedal stroke to cause the device to determine that the switch is turned ON. Another point to note about the following processing device is that the accelerator pedal is moved to move the vehicle forward as controlled through the device. This presents a new problem to the configuration using the accelerator pedal as the operation switch. That is, especially when the accelerator pedal is mechanically connected to a throttle valve, it is necessary to set a pedal stroke that causes the device to determine that the switch is turned ON larger than the pedal stroke that occurs under the control of the following processing device. It is necessary that the pedal stroke causing the device to determine that the switch is turned ON be set adequately large. To dissuade the driver (user) from being hesitant about depressing the accelerator pedal in such cases, it would be necessary to offer a new means or the like that would let the driver (user) know that the traffic congestion following device is being activated and that the host vehicle will not jump forward even when the accelerator pedal is depressed.